Bi-polar acrivating particles for electrodeposition process

ABSTRACT

An electrically-conductive mass in the form of a small particle encapsulated in a hard non-conductive outer sheath having at least one opening in such sheath permitting contact between such conductive mass and a liquid electrolyte when the particle is immersed in such electrolyte. Preferably, the conductive mass and/or the outer sheath is so formed or treated that the conductive mass does not protrude beyond the sheath at any of said openings.

United States Patent 1191 1111 3,847,660

Eisner Nov. 12, 1974 [5 1 Bl-POLAR ACRIVATING PARTICLES FOR 3,518,1ll6/1970 Wright 117/100 M ELECTRODEpOSITION PROCESS 3,389,l05 6/1968Bolger ll7/l00 M 3,694,243 9/l972 Campbell ll7/IOO M [75] lnvcntor:Steve Eisner, Schenectady, NY.

[73] Assignee: Norton Company, Troy, NY. primary Examiner LcOn D. Rosdm2 I Filed; May 3 97 Assistant ExaminerMichael F. Esposito Attorney,Agent, or Firm-Hugh E. Smith [21] Appl. No.: 258,421

Related U.S. Application Data Division of Ser. No. 147,409, May 27,1971, Pat. No.

U.S. Cl 117/212, 117/230, 204/45 R, 204/49, 204/52 R, 204/DIG. 10,204/279 Int. Cl B44d 1/18, B44d l/34 Field of Search ll7/2l2, 100 M,230, 201; 204/52 R, 45, 49, 279, 242, DIG. l0

References Cited UNITED STATES PATENTS 4/1972 Longo ll7/l00 M 5 7ABSTRACT 4 Claims, 4 Drawing Figures BI-POLAR ACRIVATING PARTICLES FORELECTRODEPOSITION PROCESS This is a division, of application Ser. No.147,409, filed May 27', 1971 now U.S. Pat. No. 3,699,017.

FIELD OF THE INVENTION The prsent invention relates to electrodepositionof metal onto a substrate from a liquid electrolyte solution by imposedcurrent flow. It is particularly adapted for use in a system such asthose disclosed and claimed in the copending applications of SteveEisner, Ser. No. 102,287, filed Dec. 29, 1970 now U.S. Pat. No.3,699,014 and of Norvell E. Wisdom, Jr., Ser. No. 140,143, filed May 4,1971 now U.S. Pat. No. 3,699,015, (which are more fully describedbelow).

DESCRIPTION OF THE PRIOR ART Particulate material of various kinds hasheretofore been incorporated into plating baths, generally with the ideathat it would polish or densify plate laid down by conventional meansand at conventional rates. Generally, this material has beenincorporated in the form of a suspension with agitation of the liquidelectrolyte serving to keep this material suspended therein. In at leastone instance, (U.S. Pat. No. 1,594,509), the particles were relativelylarge and motion of the container served to cause these materials tobeat or pound the plate after it was deposited to densify the plate. Inall of this type of art, an extremely low particle to liquid volumeratio was employed. More recently, French 1,500,269 recognized thatincorporating a relatively high'volume of particles to liquid in theform of a fluidized bed caused a reduction in cell voltage at constantrelatively low current densities in a specialized plating system ascompared-with the voltage resulting from high flow rates of electrolyteonly. This patent also suggests that conductive particles could be usedif desired. Conductive particles have also been used to form fluidizedbed electrodes in work sponsored by the National Research andDevelopment Council in Great Britain. Still more recently, theaforementioned processes described and claimed in U.S. applications,Ser. Nos. 102,287 now U.S. Pat. No. 3,699,014 and 140,143 now U.S. Pat.No. 3,699,015 have recognized that going to veryhigh particle to liquidratios and utilizing externally applied vibratory forces to set andmaintain small, hard particles in motion over the surfaces of thearticle being plated throughout the entire period of imposed currentflow permitted some material improvements in plating rates in the caseof Ser. No. 102,287 now U.S. Pat. No. 3,699,014 and in throwing power inthe case of Ser. No. 140,143 now U.S. Pat. No. 3,699,015. The throwingpower improvement of this latter case is achieved at the expense ofimproved speed of deposit although rates equivalent to or slightlygreater than conventional can still be achieved. As is covered in detail in such application, the throwing power improvement is obtained byso arranging the system as to bring into the plating zone electrolyteessentially solely as a surface layer on each individual particle. Theprocess of Ser. No. 102,287 now U.S. Pat. No. 3,699,014, on the otherhand, has electrolyte present in all of the interstices between theactivating particles in the plating zone as well as on the surfacesofsuch particles, and does achieve substantial increases in plating ratesboth over conventional processes and over the process of Ser. No.140,143 now U.S. Pat. No. 3,699,015 as a result. The throwing power ofthe process of Ser. No.

102,287 now U.S. Pat. No. 3,699,014, however, is not time intervals witha plurality of small dynamically hard particles. Activating the surfacemeans so treating the surface as to create at such surface a hightendency to utilize the imposed current to deposit metal in sound,adherent form rather than as powder or dendrites. Dynamically hard isdefined to mean that the particles act, through a combination of theiractual hardness, mass, impact speed and pressure, in such a manner as toactivate the electrodeposit surface and generally a criteria of thishardness is the formation in the surface of the deposit of visiblescratch patterns (visible at least under a magnification of 10,000X orless). The particles are placed in a container capable of being vibratedby externally imposed forces which imparts both a macroand amicro-motion to such particles as a result of impacts between suchparticles and the walls of the container. Electrolyte is placed in suchcontainer along with the particles with the electrolyte level beingabove or at least substantially filling the plating zone in the case ofthe process of Ser. No. 102,287 now U.S. Pat. No. 3,699,014 and below orjust barely into such zone in the case of the process of Ser. No.140,143 now U.S. Pat. No. 3,699,015. Motion is initiated in eachinstance before any current flow is imposed and such motion is continuedthroughout the plating cycle. Generally, the cathodic part being platedis fixtured in the container although it can be arranged so as to movetherethrough in a predetermined and fixed path. In both of theseprocesses, the particles are entirely or at least predominatelynon-conductive electrically. It is possible, as disclosed in theseaforementioned applications, to use a small amount, i.e., up to about 5percent by volume of conductive particles along with the major portionof non-conductive particles. The present invention is directed to a typeof conductive particle which can be used as the sole particle type inprocesses such as those described above.

SUMMARY The present invention involves the discovery that two problems"involved in the activating particle-vibratory container processesdiscussed above can be solved by the use of-a particular type ofactivating particle. First, in such a process, the extremely high volumeof particles to electrolyte tends to create a serious interference withcurrent flow between the anodes and the cathode the particles serving tocause a plurality of tortuous, interrupted paths for such current tofollow. Secondly, whereas the volume of; electrolyte in one instance issufficiently high to permit rapid deposition rates, throwing power isnot improved. In the other instances where throwing power is improved,the electrolyte volume is so low as to limit the speed to essentiallyconventional rates. It would be desirable to increase the throwing powerwithout this decrease in plating rate.

By using as the activating particles a composite particle having a bodyor core portion formed of electrically conductive material (usually butnot necessarily the same metal as is intended to be deposited) with aprol'is a view in tective outer covering or sheath or non-conductivematerial which is sufficiently hard as to permit the particle to actdynamically hard, (generally such sheath must have a Knoop hardness ofabout 500 or greater) where such outer sheath is perforated or open atleast at one point on the surfaceof the particle to expose the metal orelectrically-conductive underlying core portion, both of the aboveproblems can be solved. The particle cores, being electricallyconductive, provide reasonably direct paths for current flow and theparticles themselves act as bi-polar electrodes the side of the exposedmetal toward the anode at any given instant tending to act as a cathodeand having metal deposited on the core with the side towards the cathodetending to act as an anode and giving up metal ions. With the high.particle density, those particles immediately adjacent the surface beingplated provide a high supply of metal ions at the point necessary toafford an adequate supply for even, uniform thickness deposition even ona contoured surface.

DRAWINGS cross section of a typical particle of ,the present invention.a

FIG. 2 is'a perspective view in partial cross section of avaria'tion inshape of a particle of the present invention.

FIG. 3 is a schematic illustration showing the relationship of particlesof the present invention to an anode and cathode.

.FIG. 4 is an idealized view schematically illustrating one current paththrough the system shown in FIG. 3 and illustrating the bi-polar effect.

DESCRIPTION OF PREFERRED EMBODIMENTS The activating particles'of thepresent invention are preferably formed with a metallic core of themetal to be deposited in the system in which the particles are to beused, i.e., for a copper plating system, the particle core is copper andfor a nickel plating system, the core is nickel. The surroundingnon-conductive sheath should preferably be of a relatively hard,impacttransmitting material, i.e., having relatively highnonenergy-absorbing characteristics. Most of the thermosetting resinsfall into this category as do the ceramic b'ondsused in and known to theart of bonded abrasives. In addition to being non-energy-absorbing andnon-conductive, the sheath should possess the property of being easilywet by the electrolyte in which it is to be used and should also beresistant to chemical attack by such electrolyte. The hardness of theouter sheath should generally be at least slightly harder than that ofthe metal to be plated but since higher hardnesses do not appear toproduce adverse effects, it is preferred,

in order to avoid experimentation to utilize for such sheaths materialshaving a hardness of about Knoop 500 or greater. For the process of Ser.No. 102,287

now U.S. Pat. No. 3,699,014, smooth surfaced particles are satisfactoryalthough particles with rough surfaces are satisfactory. However, in theprocess of Ser. No. 140,143 new U.S. Pat. No. 3,699,015, where theelectrolyte in the plating zone (once movement of the particles isinitiated) is carried into such zone on the surface of the particles, amicro-roughness is an essential feature of the particle surface.

Suitable materials for forming the particles of the present inventioninclude, as indicated above, any conductive material which will accept ametal deposit thereon and preferably the specific metal which theparticle is to be used to help deposit. These include all of theconductive metals which-are capable of electrodeposition. As to thesheath, the preferred coating is a ceramic such as aluminum oxide,silicon carbide, boron carbide or the like, and again, preferably, suchcoating will have embedded therein or anchored thereby a plurality ofvery small particles of any of the conventionally-used abrasivematerials such as silicon carbide, aluminum oxide, flint, emery, garnetor the like. These very small particles in the sheath will generallyhave an average diameter in the vicinity of l to l0 microns. Also,thermosetting resins, resistant to the electrolyte with which theparticles are to be used, may also be used to form the sheath eitheralone or again with the occulsion of small abrasive particles. Examplesof such resins include phenolics, polyesters, ureaformaldehyde resins,polyethers, polyamides or the like.

The size of the particles in the present invention should generally bein the rangeof 0.01 to 0.25 inches in average maximum dimension with thepreferred range being between 0.02 and 0.125 inches. Particles ofvarying sizes and shapes may be blended together to vary the degree ofactivation of the electrodeposit if desired.

The shape of the particles may vary within wide limits from extremelyirregular to very uniform geometric shapes. Preferably, for ease information, the particles are in the shape of short cylinders although asis illustrated in FIG. 2, more complex shapes are contemplated and maybe particularly desirable in some instances.

Referring now to the drawings, FIG. 1 illustrates in cross section apreferred form of the particles of the conductive sheath 12 is a ceramiccoating containing.

small abrasive grains. The particle is formed by coating a continuoussmall-diameter metal wire or rod with a ceramic mixture, fusing theceramic to cause it to harden and become permanently bonded to the wire,and then severing the coated wire at short intervals to produce shortcoated cylinders open at each end. The particles are then immersed in anetching solution, e.g. nitric acid for copper core particles, and leftfor approximately 1 to 2 seconds with mild agitation to cause theexposed wire cores to be etched or eaten away. This produces a particlewith the metal core inset as shown at 13 in FIG. 1 whereby directelectrical contact from one particle to another is minimized orprevented. This prevents any shorting across the particle path fromanode to cathode in the plating system.

FIG. 2 illustrates a modified version of the invention wherein theparticle 20 is a doughnut shape. Again, a metal or conductive core 21 ispartially encased in a sheath 22. Here the sheath 22 is illustrated as ahard resin coating which provides incremental covering sections 22around the outer periphery of the core 21 and additional coveringsections 23, not necessarily corresponding to 22, around the innerperiphery of core 21. As shown, the sheathedcore particle has an opencentral portion 24 which provides more room for electrolyte movement andadditionally increases the surface area of the particle 20 exposed tosuch electrolyte over that available with a solid particle of the sameexternal dimensions. Portions of the core 21 are exposed between theouter 'sheath segments 22 as shown at 25 and between theinner sheathsegments 23 as shown at 26.

ln'operation, these particles, in accordance with the processesdescribed in the aforementioned copending applications, are literallypacked in very close relationship to one another in the plating systemsubstantially completely filling the space between the anode and cathodeas-is illustrated in FIG. 3 (as indicated in the said copendingapplications, the difference between the number of particles in theplating zone with the system at rest and with vibration imposed on thesystem is not greater than 5 percent). FIG. 3 schematically shows aportion of a plating sytem having a nonconforming anode and a contouredcathode 31. Interposed between anode 30 and cathode 31 is a plurality ofvarying sized particles 32 shown here in cross section to illustrate theconductive core 33 and protective non-conductive sheath 34. Although theelectrolyte is interspersed throughout the interstices between particles32, it is difficult toillustrate-and hence is indicated only at 35(above the illustration of the particles 32) with the understanding thatactually the particles 32 completely cover the entire cathode surfaceduring plating and are either interspered with the electrolyte 35 orcarry the same on-their outer surfaces. It will be noted that noparticular orientation of these particles can be observed and actuallythey tend to both rotate in their micro-orbits and move relative to theanode and cathode in their macro-orbit throughout the plating cycle sothat their orientation to one another and to the fixed anode and cathodeis constantly changing under the imposed external vibration. As shown inFIG. 3, an electrodeposit 36 is forming on cathode 31 and, because ofthe bi-polar effect of these particles, such deposit 36 is relativelyuniform in thickness despite the varying contours of cathode 31 uponwhich it is being deposited.

FIG. 4 schematically illustrates the function of the particle structureof the present invention. Again a cathode 40 and anode 41 is provided inan electrolyte 42. An idealized single chain of particles 43 is shown topermit clear illustration. Each particle 43, as shown, has the recessedconductive core portion 44 and the surrounding non-conductive sheath 45.It is clear that current flow between the cathode 40 and anode 41 willtake place from the electrode to the electrolyte, through the conductivecore of a particle to the electrolyte, through the next particle core,etc., until the other electrode is reached. If these were allnon-conductive particles, the current flow would obviously have to bethrough the electrolyte only and the path of such flow would be muchmore indirect with consequent loss of efficiency and increase in the IRheating of the electrolyte. Also shown in this diagrammatic illustrationis the bi-polar effect. At any given instant the particles will have afixed orientation to one another and to the electrodes. What is shownhere is a look at this particular lyte. This is continued across thechain as illustrated by V the bracketed positive and negative signsuntil the surface of the electrodeposit 46 is reached. At that point,the core portion 44 of the particle 43 closest to the cathodicelectrodeposit surface 46will act anodically and will tend to give offmetal ions extremely close to the electrodeposit surface. This readysupply of metal ions in close proximity to the surface activated by theimpact of the particles 43 causes the plate to build up uniformlydespite the varying contours of the surface of the cathode 40.

EXAMPLE 1 Using a 1/64 inch diameter copper wire as the coreforrningmember, particles according to the present invention can be prepared bysuspending 12 inch long sections of such wire inside l/32 inch diameterholes in a graphite block. The lower portion of the block is thenimmersed in a bath of molten alumina. A vacuum is then pulled on theholes and the molten alumina flows up and around the wire sectionsinside the graphite block. The block is then broken into sectionsbetween the wire segments and is burned to remove the coated wiresegments. Using diamond saws, the ceramic coated wire is then cut into1/32 inch long pieces which may be used as is for the purposes of thepresent invention or preferably after a short etching with concentratednitric acid to insure that the metal core is recessed inside the ceramicsheath. If desired, the small pieces may be pre-tumbled before using inone of the described electrodeposition processes in order to roughen thesurface of the alumina.

EXAMPLE 2 Another manner in which particles of the present invention maybe prepared is exemplified by the preparation of a slurry of fineabrasive grain (Grit 1,000 Silicon Carbide) in a thermosetting phenolicresin binder. Such slurry preparations are well known in the abrasiveart and the viscosity will be adjusted as desired to provide for sprayor dip application. Preferably, the wire to be coated l/64 inch nickelwire) is passed in continuous form through a bath of this slurry andslowly rotated in a forced hot air draft for about one hour to permitthe resin to set up slightly. The wire is then passed into an ovenheated to about 300F. for 256-3 hours to cause the resin coating tocure. After curing to a hard state, the coated wire is cut into short(l/32 inch) segments by diamond saws, etched by a 1-3 second immersionin concentrated nitric acid, given a thorough Water wash and then isready for use in an electrodeposition process.

EXAMPLE 3 3,500 cc of the bi-polar activating particles of Example l(etched to recess the metal core portions) were combined with 6,000 ccof copper sulfate plating solution (300 grams/liter CuSO .5H O andgrams] liter H SO4 containing 0.5 percent by volume of UBAC No. l-acommercially available brig lrteper for copper). The mixture was thenplaced in a /3 cubic foot capacity vibratory finishing machine (ElliotVibratub). The cathode was a steel doorknob to which a copper strike hadfirst been applied. The doorknob was mounted in a vertical position withthe knob end upwards and surrounded by four equally-spaced /2 inchsquare copper bars which acted as anodes. The bars formed a hollowsquare with the doorknob in the center with approximately 1 inchdistance between the cathode and each anode bar. Plating was carried outwith the Vibratub operating at 2,100 cycles per minute with a tubamplitude of Vs inch. A current of 50 amps was applied which calculatedout to a current density of approximately 750 amps/ft. at the cathode.Plating was carried out for 2 minutes at the end of which a smooth,uniform copper plate of 1.2 i 0.1 mils was obtained over the entiredoorknob. Plating an identical doorknob under the same conditions bututilized as the activating particles non-conductive Grit 30 sinteredbauxite particles gave a plate of similar appearance but one whichvaried in thickness from 0.7 mils on the shank to 2.4 mils on the outercurve of the head portion.

In addition to forming the particles as illustrated in Examples 1 and 2above, ceramic coatings can be applied by co-extrusion of the metal corewith a ceramic mix or by swagging or rolling the wire in a fine grainceramic mix followed by encasing the coated wire in a metal sheath whichis dissolved or cut away after sintering the ceramic. Also, in the caseof resin coatings, the slurry can be sprayed onto the wire or applied bycoating rolls if desired. Cylindrical particles can be obtained byrolling metal balls in a slurry and after the resin mixture has set up,abrading away the resin sheath on one surface of the balls.

I claim: 1. A bi-polar conductive particle for use in electrochemicalprocesses which comprises:

a. a conductive metal core member; and b. a hard, non-conductive sheathcompletely encapsulating said core member except at diametricallyopposed openings therein which permit contact between such conductivecore and a liquid electrolyte when the particle is immersed in suchelectrolyte; c. said core member being recessed at said openings in saidnon-conductive sheath.

2. A particle as in claim 1 wherein said nonconductive sheath is formedfrom a ceramic material.

3. A particle as in claim 1 wherein said nonconductive sheath is formedfrom a thermosetting resin.

4. A particle as in claim 1 wherein a plurality of small, hard,non-conductive particles are embedded in the material forming saidnon-conductive sheath.

1. A BI-POLAR CONDCUTIVE PARTICLE FOR USE IN ELECTROCHEMICAL PROCESSESWHICH COMPRISES: A. A CONDUCTIVE METAL CORE MEMBER; AND B. A HARD,NON-CONDUCTIVE SHATH COMPLETELY ENCAPSULATING SAID CORE MEMBER EXCEPT ATDIAMETRICALLY OPPOSED OPENINGS THEREIN WHICH PERMIT CONTACT BETWEEN SUCHCONDUTIVE CORE AND A LIQUID ELECTROLYTE WHEN THE PARTICLE IS IMMERSED INSUCH ELCTROLYTE; C. SAID CORE MEMBER BEING RECESSED AT SAID OPENINGS INSAID NON-CONDUCTIVE SHEATH.
 2. A particle as in claim 1 wherein saidnon-conductive sheath is formed from a ceramic material.
 3. A particleas in claim 1 wherein said non-conductive sheath is formed from athermosetting resin.
 4. A particle as in claim 1 wherein a plurality ofsmall, hard, non-conductive particles are embedded in the materialforming said non-conductive sheath.